1. Field of the Invention
The present invention relates to a disk gripping device most suitably applied to, for example, a floppy disk apparatus.
2. Description of the Related Art
Conventionally, a disk gripping device shown in FIGS. 1 to 6 is used for a floppy disk apparatus.
As shown in FIG. 4, this prior art device is arranged such that a turntable 2 is horizontally secured to the outer circumference of a vertical shaft 1, at a position lower than the upper end of the shaft 1 and rotated by a motor (not shown) so that the turntable 2 is integrally rotated with the shaft 1, and a magnetic plate 3 and a friction plate 4 as a sliding sheet are mounted on the upper surface of the turntable 2 at different heights around the outer circumference of the shaft 1. Further, a swingable member 5 disposed along the lower surface of the turntable 2 is mounted on a fulcrum pin 6 downwardly and vertically fitted into a fulcrum hole 7 provided in the above turntable 2 by press fitting or the like. More specifically, the swingable member 5 is secured to the turntable 2 so that it can rotate about the fulcrum pin 6 in the directions of arrows a and b in FIG. 5B, and is pressed against the lower surface of the turntable 2 by an elastic member 8 having a leaf spring structure (FIG. 4) and fitted to the fulcrum pin 6 at the lower portion of the swingable member 5. A drive pin 9 composed of a bearing vertically secured to the swingable member 5 is fitted into a through hole 10 defined in the turntable 2 and projected to substantially the same height as the shaft 1 above the turntable 2. A leaf spring 11 integrally formed with the swingable member 5 by pressing is biased by a pin secured to the lower surface of the turntable 2 so that the swingable member 5 is urged in the direction of an arrow a in FIG. 5A by the elastic force of the leaf spring 11.
Note, as shown in FIG. 5A, before a floppy disk 14 is gripped, the swingable member 5 is urged in the direction of the arrow a about the fulcrum pin 6 by an elastic force of the spring 11, so that the drive pin 9 secured to the swingable member 5 abuts against the peripheral edge 10a of the through hole 10 of the turntable 2 to be positioned.
Next, when the floppy disk 14 is gripped, the core 15 of the floppy disk 14 as a disk-like recording medium is horizontally mounted on the turntable 2 as shown in FIG. 4 in a state that the turntable 2 is rotated in the direction of an arrow c by the shaft 1, as shown in FIGS. 3 and 4.
At that time, the shaft 1 and the drive pin 9 are fitted into a substantially square-shaped central aperture 16 defined at the center of the core 15 composed of a magnetic substance and a substantially rectangular positioning aperture 17 defined at the outer periphery of the core 15 and having a lengthwise direction inclined by a predetermined angle with respect to the central aperture 16, respectively, and thus the core 15 is horizontally and magnetically gripped on a friction plate 4 of the turntable 2 by the magnetic plate 3.
When the turntable 2 is rotated in the direction of the arrow c at a high speed after the floppy disk 14 is gripped, the floppy disk 14 is rotated in a cassette (not shown) in the direction of the arrow c at a high speed by the drive pin 9 through the core 15. Then, a pair of upper and lower magnetic heads (not shown) in contact with both the upper and lower sides of the floppy disk 14 scan the floppy disk 14 in the radial direction thereof to carry out a desired recording and reproduction. At that time, a loss torque Y is produced in a direction (the direction of an arrow d) opposite to a rotating direction of the turntable 2 (the direction of the arrow c) by frictional forces produced between the floppy disk 14 and the magnetic heads and between the floppy disk 14 and a liner (not shown) in the cassette.
Therefore, the drive pin 9 is guided to the outer periphery 17b of the positioning aperture 17 and in the direction approaching the shaft 1 of the turntable 2, with the result that the swingable arm 5 is rotated in the direction of the arrow b in FIG. 3 against the leaf spring 11. Accordingly, the drive pin 9 is pressed against the forward-side edge 17a (rotating in the direction of the arrow c) of the rectangular positioning aperture 17 of the core 15 and the peripheral-side edge 17b thereof perpendicular to the forward-side edge 17a, by vertical forces F.sub.1, F.sub.2, respectively. Two edges 16a, 16b of the central aperture 16 of the core 15, which are at right angles to each other, are pressed against the circumference of the shaft 1 by forces R.sub.1, R.sub.2, which are reaction forces of the vertical forces F.sub.1, F.sub.2, and as a result, the core 15 is positioned with respect to the shaft 1 by a resultant force having a line of action coinciding with a diagonal P1 of the substantially square-shaped central aperture 16.
Note that the following equations are obtained, assuming that a center line passing through the center O.sub.1 of the shaft 1 and the center O.sub.3 of the fulcrum pin 6 is a Y-coordinate axis, a coordinate axis passing through the above center O.sub.1 and intersecting the Y-coordinate axis at right angles is an X-coordinate axis, P.sub.2 represents a center line passing through the center O.sub.2 of the drive pin 9 and the center O.sub.3 of the fulcrum pin 6, l represents a distance between the centers O.sub.2 and O.sub.3, .theta. and .phi. represent angles between the center line P.sub.2 and the Y-coordinate axis and the diagonal P.sub.1 and the Y-coordinate axis, respectively, and further, F.sub.3 represents an initial positioning force applied by the spring 11 to the drive pin 9, as shown in FIG. 5B. EQU F.sub.1 =T/l.multidot.sin .theta. (1) EQU F.sub.2 =T/l.multidot.cos .theta.+F.sub.3 ( 2) EQU .phi.=tan.sup.-1 (F.sub.2 /F.sub.1) 60.sup.o ( 3)
An ideal gripping can be provided by designing the disk gripping device satisfying the above equation (3).
Nevertheless, since this kind of disk gripping device is arranged such that the fulcrum pin 6 is fitted into the fulcrum hole 7 of the swingable member 5, to enable the swingable member 5 to be rotated in the direction of the arrows a, b about the fulcrum pin 6, a fit clearance between the fulcrum pin 6 and the fulcrum hole 7 cannot be made substantially zero, and when observed on an enlarged scale, a fit clearance 18 exists between the fulcrum pin 6 and the fulcrum hole 7, as shown in FIGS. 5A and 5B.
Moreover, as shown in FIGS. 5A and 5B, the leaf spring applies a load F.sub.3 to the swingable member 5 in a direction substantially parallel to the center line P.sub.2, in such a manner that the direction is inclined by an angle .theta., to the direction in which the turntable 2 is rotated (the direction of the arrow c) with respect to the center line x' of a pin 12, which is parallel to the X-coordinate axis, so that the swingable arm is urged in the direction of the arrow a.
Therefore, as shown in FIG. 5A, when the floppy disk 14 is gripped, a contact point P.sub.3 of the fulcrum hole 7 with the fulcrum pin 6 conventionally tends to be moved in the direction of an arrow e, which is opposite to the drive pin 9 with respect to the center O.sub.3 of the fulcrum pin 6.
On the other hand, after the floppy disk 14 is gripped, the above contact point P.sub.3 tends to be moved in the direction of an arrow f, which is nearer to the drive pin 9 with respect to the center O.sub.3 of the fulcrum pin 6, because the swingable member 5 receives the loss torque T in the direction of the arrow d in FIG. 5B. After the floppy disk is gripped, however, the position of the above contact point P.sub.3 is changed with a change of the loss torque T and a coefficient of friction of the core 15 to the friction plate 4.
Therefore, conventionally, when the floppy disk 14 is mounted on or dismounted from the turntable 2, a position of the above contact point P.sub.3 is liable to be greatly changed in the direction of the arrows e, f along the outer periphery of the fulcrum pin 6, by a difference D between the diameters of the fulcrum pin 6 and the fulcrum hole 7 as shown in FIG. 6, and a large amount of change .DELTA.l corresponding to the above clearance 18 is liable to be incurred at the arm length l of the swingable member 5 after the floppy disk is gripped, as shown in FIG. 5B.
When the large amount of change .DELTA.l is incurred at the arm length l, a location at which the core 15 is positioned with respect to the shaft 1 is changed in the circumferential direction, to thus change an index position recorded on the floppy disk 14 in the circumferential direction, and therefore, a serious problem arises in that the index position cannot be read.
Further, a problem arises in that, since the turntable 2 and the fulcrum pin 6 are arranged as separate parts, the number of parts is increased accordingly and the fulcrum hole 7 (FIG. 4) must be defined in the turntable 2, to enable the fulcrum pin 6 to be attached thereto.
Furthermore, after the fulcrum pin 6 is fitted into the fulcrum hole 7, a process for fixing the extreme end of the fulcrum pin 6 by a screw or caulking, or the like, is also needed. In addition, a problem arises in that an accuracy of the center of rotation of the swingable member 5 is lowered due to a positional dislocation caused when the fulcrum pin 6 is secured to the turntable, and the insertion of the elastic member 8 of the leaf spring structure into a narrow space between the swingable member 5 and the flange provided at the lower end of the fulcrum pin 6 is very difficult, and the like.